| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 100 === To simplify the element of bismuth telluride thermoelectric materials, the experiments reported in this study used Te as the substrate to evaluate the capability of Ni as a diffusion barrier. Ni-P or Ni-P/Co-P was coated on Te by electroless plating and then jointed to observe interfacial reaction with Sn solder. Ni has been widely used as a diffusion barrier between Sn-based solder and chip in electronic industry. Ni3Sn4, Ni3P, and NiTe are the major compound layers formed at the Sn/Ni-P /Te interfaces. The apparent activation energy of NiTe in a Ni-P/ Te system is 70.9 kJ/ mol. The Ni3P layers formed both at the Ni/Sn and Ni/Te interfaces, with columnar voids embedded in Ni3P. The number of columnar voids at the Ni/Te interface is greater than that at the Ni/Sn interface. The larger Ni flux caused a greater unbalance interdiffusion and induced more voids formed at the Ni/Te side. To inhibit the flux of Ni toward the Te side, a layer of Co was selected as the diffusion barrier. The Co-P was electroless plated between the Ni and Te substrate. In Sn/Ni-P/Co-P/Te couple, Co-Te IMC was not found between Co-P and the Te interface at all annealing temperatures. A very thin Ni-Te IMC layer formed between Co-P and Te at 180℃ for 240 h. At 450 K, the formation Gibbs free energy of NiTe and was -1.78 kJ/mol and lower than that of CoTe2 was -0.86 kJ/mol, suggesting that the formation of Ni-Te IMC was energetically favorable. At all annealing temperature, Ni3P and columnar voids did not appear at the Ni-P/Co-P/Te interface. These results prove that Co is an effective diffusion barrier suppressing the growth of Ni3P and thereby preventing voiding problems. Finally, the Co-P barrier enhanced the quality of the solder joint because it suppressed the formation of Ni-Te IMC and large voids.
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